Significant infection with cytomegalovirus (CMV) is serious in immunocompromised patients, particularly those who have undergone allogeneic bone marrow transplantation (ABMT), and in patients with AlDS. For ABMT patients, both culture from blood buffy coats and blood antigenemia assay are used to determine the need for anti-CMV therapy. If either test is positive, the patient is presumed to have disseminated CMV disease. For AlDS patients, it is less clear which diagnostic laboratory tests provide useful predictive value, and more data are needed to determine the utility of blood CMV cultures as well as blood antigenemia testing. CMV polymerase chain reaction (PCR) can provide more sensitive detection of CMV in blood than either culture or antigenemia. Although several commercial PCR tests are being developed, none are currently available for use. We have therefore embarked on the development of a blood PCR test for potential use on Clinical Center patients. For this development, we needed to optimize the PCR assay particularly with regard to processing and preparing blood for sensitive detection of CMV DNA and for elimination of PCR inhibition from the specimen. Although the assay works well in specimens spiked with known amounts of CMV, it needs to be further tested to determine its sensitivity for detecting CMV in peripheral white blood cell pellets from patients known to be infected with CMV. Once the assay is working reliably with good sensitivity, we will follow patients with positive CMV PcR assays to determine how this reaction correlates with culture and antigen assays and with clinical disease progression.